Smokeless powder manufacture



Sept. 7, 1965 D. H. BLACK SMQKELESS POWDER MANUFACTURE Filed June 8, 1946 FIG.2

FIG.

DONALD H. BLA C K INVENTOR.

AGENT United States Patent 3,205,286 SMOKELESS POWDER MANUFACTURE Donald H. Black, Cumberland, Md., assignor, by mesue assignments, to the United States of America as represented by the Secretary of the Army Filed June 8, 1946, Ser. No. 675,436 16 Claims. (Cl. 264-3) This invention relates to the manufacture of smokeless powder and, more particularly, to improvements in the process for producing large smokeless powder propellants by the casting technique.

Smokeless powder propellants suitable for propelling military rockets or actuating sizeable jet devices such as assisted takeoff motors for airplanes are normally formed so as to present a relatively small amount of burning surface, and so keep the rate of gas production at the required low level. Propellants as large as 4 to 5 inches in diameter are commonly used for this purpose and are generally made by the well-known solventless extrusion procedure which comprises rolling sheets of colloided smokeless powder into tight rolls and pressing the rolls, at an elevated temperature, through a precision die. This procedure requires specialized and expensive equipment and is quite hazardous due to the high pressure and elevated temperatures utilized and the ever present danger of fire associated with the rolling of the powder prior to extrusion. Furthermore, extrusion presses now in use are limited to the production of propellants having a maximum diameter of 4 to 5 inches. Hence, the production of larger propellants, for which the demand is steadily increasing, would require the use of more massive presses than are now available.

More recently, an extremely simplified method of fabricating large, cast propellants of almost any size and shape has been developed. This method comprises essentially the cementing together of smokeless powder granules of conventional shape and siZe by a mixture of nonvolatile explosive and nonexplosive plasticizers. The components are introduced into a container of suitable size and shape by increments, the mixture being agitated after the addition of each increment to insure packing and to remove air. The mixture is then cured at an elevated temperature until the granules have absorbed the plasticizers, swollen and set in a single, hard, compact mass. This method requires no specialized and expensive equipment, such as is needed in solventless powder manufacture and is inherently less hazardous than solventless extrusion, since the powder is not subjected at any time to the simultaneous effects of high pressures and elevated temperatures. Moreover, the fire hazards associated with the rolling of powder prior to solventless extrusion are not encountered. Additionally, the casting procedure makes it comparatively simple to incorporate burning rate control material in the form of filaments or tiny granules and to inhibit the burning surface by casting the ingredients in a uonflammable container.

In order to produce a cast smokeless powder propellant which is homogeneous throughout and free of air bubbles or fissures, it is essential that the casting powder granules,

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burning rate control particles, and plasticizer be combined in such a way that they are uniformly distributed throughout the casting. The method heretofore used, involving the addition and agitation of successive increments of the powder component, has not been entirely satisfactory in these respects with the result that the casting may contain entrapped air bubbles and/or local concentrations of nonvolatile plasticizer, casting powder, or burning rate control particles. These factors cause fluctuations during burning and can lead to uncontrolled fast burning, with the development of high pressure and possible rupture of the combustion chamber walls.

Now, in accordance with this invention, it has been found that large, cast smokeless powder propellants, having uniform rates of burning, may be produced in a simpler and more effective manner by placing the casting powder and, if desired, burning rate control powder in a suitable casting container and introducing the plasticizer into the lower portion of the container. Propellants cast in accordance with this method have better uniformity in chemical composition and physical properties throughout various sections of the casting than those cast by methods used heretofore.

Generally described, the present invention comprises mixing granules of suitable casting powders and, if desired, burning rate control powders into a homogeneous mass of powder granules, introducing the mass of powder granules quickly and at an even rate into a suitable casting container, placing a vented weight on top of the powder to hold it in place, and then admitting nonvolatile plasticizers through an opening in the base of the container. As the plasticizer slowly rises in the container, it forces the air upwardly through the top thereof and completely contacts and surrounds the individual powder granules. The vented weight holds the powder granules in place but permits the displaced air to escape. When sufiicient plasticizer has been admitted to leave a layer of liquidat least 0.1 inch deep on top of the powder, the opening in the bottom of the container is closed off and the vented weight removed. The charge is then cured in suitable apparatus such as a forced air oven, removed, and cooled. The cast propellant so produced is homogeneous and completely free of entrapped air bubbles. Tests show that it has a very uniform burning rate.

In an alternative procedure, the burning rate control powder is incorporated in the cast propellant in the form of strands or filaments. The strands or filaments, held in spaced relation by upper and lower perforated discs, are placed in the casting container and the casting powder poured in around them. The plasticizer is then admitted through the bottom of the container as before.

Having now indicated in general the nature and purpose of the present invention, there follows a more detailed description of the invention with reference to the accompanying drawing wherein FIG. 1 is a diagrammatic view illustrating the step of filling the casting container with powder; FIG. 2 is a diagrammatic view illustrating the step of admitting the liquid plasticizer to the casting container; FIG. 3 is a diagrammatic view of a container showing a modified form of burning rate control powder and FIG. 4 is a diagrammatic view illustrating the step of admitting the plasticizer to the casting container of FIG. 3.

Referring now to FIGS. 1 and 2 of the drawing, the hopper 1 contains a charge of powder 2 which is a homogeneous, granular mass obtained by mixing, in a sweetie barrel or similar apparatus, granulated, solventextruded casting powder and burning rate control powder of suitable formulations. The powder 2 is discharged from the hopper 1 through a valve controlled outlet 3 into the casting container 4. Container 4 is preferably made of a nonfiammable plastic material, such as cellulose acetate, and is provided in its bottom portion with a central, threaded aperture 5 covered by a screen 6 to prevent the powder 7 from passing through the aperture. A nipple 8 is threaded into the aperture 5 and has on its lower end a valve 9. For the handling of nitroglycerin a wood clamp or similar device is preferably utilized as the valve.

After the container 4 is filled, a vented weight 10 is placed on the powder therein to pack and hold it in place in the subsequent operation. The container is then moved to a support 11 and connected with the plasticizer tank 12 through the valve 9, rubber tubing 13 and tank outlet 14. Tank 12 is located above the container a sufiicient height to give the desired pressure head of about 7 feet.

Sufficient plasticizer is then admitted to the container 4 to entirely fill all air spaces throughout the powder column and leave a layer of liquid about 0.1 inch deep on top thereof. The average rate of flow of the plasticizer is regulated so as to approximate about 2 pounds per minute.

The Valve 9 is then closed, and the rubber tubing pinched shut and disconnected. The weight 10 is removed and the charged container placed in a forced air oven for about 40 hours at 60 C. The cured or cast charge is removed, cooled, and the pipe nipple 8 and valve 9 removed and replaced by a cellulose acetate plug.

Referring to the modification of the invention shown in FIGS. 3 and 4, the container 15, nipple 16, and valve 17 are identical to the elements 4, 8, and 9 of FIGS. 1 and 2. However, the burning rate control powder is incorporated in the form of filaments or strands rather than granules as before. According to this embodiment, a plurality'of strands 18 of burning rate control powder are cemented in spaced relation in a perforated cellulose acetate disc 19 provided with a centrally located aperture 20 covered by a screen 26. A similar perforated disc 21 is located at the opposite end of the strands 18, but here the strands are not cement-ed into the perforations since the disc is to act only as a temporary movable spacer. The assembly of strands is placed in the casing, and the desired amount of casting powder poured in around them. The spacer 21 is then lowered onto the powder, the container moved to a suitable support 22, and a vented weight 23 placed on the spacer. Valve 17 is then connected to the rubber tubing 24 and plasticizer tank 25 as before and sufficient plasticizer admitted to the container to cover the powder. The charged container is then cured in a forced air oven, removed and cooled, and the nipple 16 and valve 17 removed and replaced by a cellulose acetate plug. The seal may then be reinforced with cellulose acetate cement and Jon-Flex tape.

In accordance with this invention and to illustrate in more particular the method of producing a cast powder propellant for use in jet-controlled applications, the following examples are given.

Example 1 Burning Casting rate, Casting powder, control solvent, percent powder, percent percent Nitrocellulose (13.15% N) 1 Added.

Both powders were made by conventional, solventextrusion methods and were granulated in the form of cylinders approximately 0.034 inch in diameter x 0.033 inch long. The powders were mixed in the ratio of 4 parts casting powder to 1 part burning rate control powder and were blended together in a revolving sweetie barrel for 20 minutes.

Referring now to FIGS. 1 and 2 of the drawing, the blend was transferred to a 12-liter wooden hopper 1 from which 2,785 g. was discharged through a 1.0 inch diameter valve-controlled outlet 3 in the bottom of the hopper, into the casting container 4. The casting container was of cellulose acetate construction, 3.75 inches inside diameter x 18 inches long. Its base had been tapped and threaded to receive a 1 inch long, 4 inch standard pipe nipple 8, one end of which was covered with a U.S.S. 40-rnesh screen 6 to prevent the powder from falling through.

The powder-filled container 4 was placed inside a desiccator and evacuated for 1 hour at a pressure of 4 mm. mercury in order to reduce surface moisture. The container was removed from the desiccator, placed on a suitable support 11, and a 50-pound weight 10 placed on the powder column. The rubber tubing 13, having an inside diameter of 0.25 inch, was connected to the valve 9 screwed onto the nipple 8, and casting solvent, which had previously been evacuated for 3 hours at a pressure of 4 mm. mercury to remove moisture and entrained air, admitted to the container from the elevated tank 12. Tank 12 was located above the container at a height to give a pressure head of 7 feet.

Sufiicient plasticizer (1585 g.) was admitted, at an average rate of 600 g./min. to entirely fill all air spaces throughout the powder column and leave a layer of liquid about 0.1 inch deep on top of the powder column. The rubber tubing was pinched shut and disconnected. The Weight 10 was removed and the charge placed in a forced air oven for 40 hours at 60 C. The cured casting was removed, and cooled, after which the pipe nipple and valve were unscrewed from the base and replaced by a cellulose acetate plug.

Five castings like the above were made. These were tested by burning them in a static subcaliber assisted takeoff motor. All castings were satisfactory in static burning tests at normal temperature. Pressures were very uniform throughout each test.

Example 2 Cast propellants of smokeless powder were made identical to those described in Example 1, with the following exceptions. After the blend of casting powder and burning rate control powder had been added to the container, the container was vibrated for 10 minutes on a mechanical vibrator having a vertical movement (amplitude 0.44 inch, frequency 194 vibrations per minute). This step packed the powder and improved the density of the finished castings. Thus, 3085 g. of powder mixture was used, and only 1394 g. of plasticizer.

Five castings like the above were made and tested by burning them in a static subcaliber assisted takeoff motor. All castings gave satisfactory results in static burning tests at normal temperature. lressures were very uniform throughout the test.

Example 3 Cast propellants were made with components having the following compositions:

Both powders were made by conventional solvent-extrusion methods. The casting powder was granulated in the form of cylinders approximately 0.034 inch diameter x 0.033 inch long. The rate control strands were approximately 0.140 inch diameter and were cut into lengths slightly greater than the desired length of the casting.

Referring now to FIGS. 3 and 4 of the drawing, 55 strands represented by 18 totalling about 1.3 pounds in weight were cemented 1 inch apart in a perforated cellulose acetate disc 19 of 8 inches diameter. A similar disc 21 was located at the opposite (top) ends of the strands but not cemented thereto.

The assembly of strands was then placed longitudinally in the casting container which was approximately 8 inches inside diameter and 30 inches long. The container had been prepared from cellulose acetate foil of 0.010- inch thickness by wrapping the foil around a mandrel until a wall thickness of about 0.12 inch was obtained. During wrapping, a stream of acetone was continuously poured overthe foil to partially dissolve it and provide the necessary strong bond. A disc of cellulose acetate, 0.25 inch thick and 8 inches diameter and having a threaded inch opening through the center thereof, was cemented into the bottom end of the cylinder and the assembled container cured at elevated temperature.

With the strands centered in the container approximately 50 pounds of casting powder (formulated as above), previously under vacuum for 2 hours to reduce surface moisture, was poured around the strands, nearly filling the container. The top cellulose acetate spacer 21 was lowered onto the powder and a -pound weight 23 placed on the spacer.

The container 15 was placed on a suitable support 22 and connected with the casting solvent tank 25 located about 7 feet above the base of the container. The casting solvent, which had previously been evacuated for about 2 hours at a pressure of 4 mm. mercury to remove moisture and air bubbles, was admitted into the container at an average rate of about 1.7 lb./min. Sufiicient liquid plasticizer (about 25 pounds) was admitted to fill all air spaces throughout the powder column and leave a layer of liquid about 0.3 inch deep on top of the powder.

The valve 17 was closed, the rubber tubing 24 disconnected, and the weight 23 and spacer 21 removed.

The charge was placed in a forced air oven for 40 hours at C. The cured casting was removed and cooled, after which the valve 17 and nipple 16 was unscrewed from the base. A cellulose acetate plug was threaded into the hole left by the stop cock and the seal was reinforced with cellulose acetate cement and Jon-Flex tape. The top 2 or 3 inches of powder, containing a higher proportion of plasticizer, was removed by horizontal sectioning. Sixtyfive castings like the above were prepared.

To evaluate the degree of homogeneity obtained in the double-base matrix, 6 one-inch cubes were cut from a slab removed from the top of each of the castings. The cubes were partially burned in a closed chamber equipped with a rupture disc which burst when a pressure of 8000 pounds per square inch was developed. The partially burned cubes were thereupon ejected into sawdust, recovered, and examined. A numerical rating based on the degree of retention of original surface smoothness was assigned to each cube and an average rating determined for the 6 cubes. The 65 bottom filled castings tested in this way showed better homogeneity than castings prepared by any of the methods of the prior art. All of the castings were considered satisfactory for firing in an assisted takeoff motor.

In order to compare the cast propellants produced in accordance with the teachings of the present invention with those produced according to methods used heretofore, the following examples are given:

Example 4 Cast propellants were made with components having the following composition:

Burning Casting rate, Casting powder, control solvent, percent powder, percent percent N itroeellulose (13.15% N) 84. 0 Nitroglycerin 15. 0 Ethyl Centralit 1. 0 Carbon Black 1 0 5 Potassium Perchlorate Triacctin 1 Added.

added, and the mold vibrated mechanically by an air vibrator (amplitude 0.03 inch, frequency 3000 vibrations per minute). When it appeared that the plasticizer had wet all of the powder, another increment of solvent approximately equal in size to the first was added, a second increment of powder was added, and the mold again vibrated to help settle and wet the powder. This operation was repeated until the mold was filled. In all, 3150 g. of powder and 1885 g. of plasticizer were used to make each casting. Castings were cured in the manner described in Example 1.

Five such castings were made and tested by burning them in a static subcaliber assisted takeoff motor. All castings showed definite flunctuations in pressure during burning in the static motor. X-ray examination of one of the castings revealed layers rich in burning rate control material and others rich in plasticizer.

Example 5 Five cast propellant charges were prepared identical to those described in Example 4, excepting that the proportion of casting powder to burning rate control powder was 4 to 1 instead of 9 to 1. These castings also showed large fluctuations in pressure during burning. Pressures became so high in one test as to rupture a safety disc and blow the nozzle oh the end of the motor.

, Example 6 Cast propellants having components identical to those described in Example 3 were prepared. After the strands had been centered longitudinally in the casting container. casting solvent, previously evacuated as described in Example 3, was poured into the container to a depth of 3 inches and approximately an equal volume-of powder,

also previously evacuated, was added. The container was swirled so that the solvent covered as much of the powder as possible, and the container was tapped on a plastic table cover in a manner used to obtain a high packing fraction. Another equal volume of powder was added and the container again tapped. About /3 of the original amount of casting solvent was added, and the tapping repeated. Special care was taken to insure that the alignment of the rate control strands was not permanently disturbed. The alternate addition of powder and plasticizer was continued until the desired amount of each had been added. When finished, there was a slight excess of liquid on top of the powder to insure a coalesced charge. Approximately 30 to 40 minutes was required to complete the loading operation. The charges were cured and trimmed as described in Example 3.

Partial burning tests on cubes prepared from about 30 castings like the above showed the homogeneity of the matrix to be somewhat less satisfactory than that of castings described in Example 3. A casting was variously sectioned and separate chemical analyses made on portions taken from different parts of the casting. Percentages of liquid plasticizer appreciably higher than the average were found in the upper parts of the casting and along the periphery. A comparison of loading times shows that the procedure of Example 3 requires somewhat less than half the time required by the procedure of Example 6.

Examples 1, 2, and 3 illustrate the improvements inherent in the procedures according to this invention.

Examples 4, 5, and 6 are illustrative of procedures commonly used heretofore in the casting of large smokeless powder propellants. A comparison of the two clearly shows the improvements in homogeneity and burning characteristics of the propellants cast in accordance with the teachings of this invention.

The preferred method of preparing cast propellants in accordance with the present invention will comprise essentially the features of adding the powder granules first in the mold, and then admitting the plasticizer through an opening in the base. Preferred casting powders, burning rate control powders, and plasticizers or casting solvents are given in the examples. It will be understood, of course, that these are given for purposes of illustration only, and that the ingredients and proportions of ingredients may be varied within wide limits without departing from the scope of the invention. It is essential, of course, that the components be compatible and lend themselves readily to casting procedures.

Buring rate control powder may be included or omitted as desired but is preferably included as set forth in the examples. If rate control material is used in the form of strands or filaments, these are positioned in the mold before the casting powder granules are added. If the rate control material is used in the form of granules, they are first blended with the casting powder. Any conventional means of thoroughly mixing or blending these components may be used, although the common sweetie barrel is preferred.

The powder next is poured into the mold. No particular care need be taken if rate control material is not present, but if it is, the powder is preferably added by pouring it vertically and at an even rate into the mold. The powder stream should not glance off the sides of the mold, or segregation of the denser rate control granules may result. Other means of filling the mold with powder without disturbing the overall distribution of rate control particles through the casting powder may be used.

At this point the powder is preferably evacuated for about 1 hour at a pressure of about 4 mm. of mercury in order to reduce surface moisture. This may be accomplished by means of a desiccator or other suitable apparatus and under conditions of temperature, pressure, and time which will give the desired result.

The powder may be packed more compactly in the mold by such means as tamping the powder, or vibrating the container. This operation merely insures a higher ratio of powder to plasticizer, and is in no way vital to the successful operation of the invention.

Before the plasticizer is introduced, the powder column should be firmly weighted to prevent any movement or displacement of the powder granules as the platsicizer courses up through the powder column. This may comprise a vented weight, as shown, or a brass cylinder fitting loosely into the top of the mold, although any sort of weight, clamp or pressure means capable of constricting movement of the powder granules would be suitable. Allowance must be made in any case for escape of the displaced air.

The liquid plasticizer is forced upwardly through the powder column under a pressure head created by raising the liquid level of the plasticizer several feet above the top of the mold. Any other means of injecting the liquid into the mold at the base at a steady rate may be employed. Pumps of all kinds, reduced pressure inside the mold, etc., could be used but all lack the simplicity afforded by the hydrostatic head. The rate at which the plasticizer rises in the mold will desirably be as great as possible without entrapping air in the powder. Upward displacements varying from about 5 to about 10 inches per minute are preferred, although rates as high as 20 inches per minute may be used, especially with larger powder granules and less viscous plasticizers than those cited in the examples.

As set forth in the examples, the casting solvent is preferably introduced into the casting through a centrally located opening of the order of 0.25 inch in diameter. It is, of course, possible to vary the location and size of the opening within wide limits so long as the casting solvent functions to thoroughly contact all powder granules and displace all air bubbles as it fills the container and Without causing any appreciable rearrangement of the granules. Thus, in an extreme case, the opening may be sufiiciently large to encompass substantially the whole area of the bottom of the container, the powder being supported on a suitable foraminous member which will permit passage of the casting solvent while holding the powder. Preferably, however, the opening will be of a size which will permit the filling of the container at the desired rate while at the same time maintaining the velocity of the introduced casting solvent below a point which would cause substantial disarrangement of the powder granules. T o accomplish this result, the opening will generally be from about inch to about 1 inch in diameter. The opening may be at any point in the bottom of the container and in some cases may even be in the side of the container closely adjacent the bottom. However, as stated above, it is preferably located centrally of the bottom of the container.

After the plasticizer has been introduced, the weight on top of the powder column is removed, the tubing disconnected, and the opening closed off to prevent the plasticizer from draining out. The casting is then placed in a heated atmosphere to cure.

Curing is desirably accomplished by placing the casting in a forced air oven for a period from about 1 hour to about 600 hours and at a temperature from about 30 C. to about C., and preferably for about 40 hours at 60 C. It will be realized, of course, that any suitable type of drying and/ or curing device may be used and that temperature and times may be adjusted and coordinated by principles well known in the art.

The cured casting is removed from the forced air oven, cooled, and the fittings removed from the base opening and replaced by a plug of suitable nonflammable material such as cellulose acetate, copper or saran. If desired, the seal may be further reinforced by means such as a nonflammable cement or a nonflammable tape, for example, cellulose acetate cement or Jon-Flex tape.

Although the casting container is preferably made of cellulose acetate, as set forth in the examples, other nonflammable materials of a similar nature may be used with satisfactory results. Such materials should have sufficient compatibility with the casting solvents used so that a strong bond between powder and container results on curing. Use of a nonfiammable container, such as cellulose acetate, inhibits the burning surface so that the charge burns endwise only.

The method of this invention is applicable to the preparation of all types of cast propellants for jet-actuated applications and particularly those in which burning rate control powder is to be present in the form of strands or randomly-distributed granules. Thus, cast propellants of various formulations and cross-sectional configurations, such as the cruciform or rosette shapes may be prepared.

This invention is also applicable to the preparation of single or multiperforated propellants which are molded or cast in containers designed to be removed before the propellant is fired. In this embodiment of the invention perforations of any size or shape can be obtained by inserting in the casting container suitably shaped metal pieces, and then withdrawing them after the casting has been cured. The removable container may be made of any suitable material which will not adhere to the powder. Suitable materials for this purpose are metal, glass and saran. mold designed to permit removal of the propellant therefrom after curing. Thus it is seen that progressive and digressive as well as uniform burning cast propellants may be made in accordance with this invention.

The method of the present invention offers many advantages over prior methods of producing large cast propellants. Thus, it is inherently less hazardous and does not require the specialized and expensive equipment needed in solventless extrusion methods. As compared to prior casting methods, the method of this invention is simpler, requires less time, and is more efficient and economical. Moreover, the resulting castings are more homogeneous, contain less entrapped air, and thus burn more uniformly and evenly. The danger of high pressures and possible blowups of the rocket or motor caused by irregular burning are thereby greatly diminished.

What I claim and desire to protect by Letters Patent is:

1. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, placing pressure on the powder granules in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

2. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a nonfiammable casting container, placing pressure on the powder granules in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

3. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a nonflammable casting container of cellulose acetate, placing pressure on the powder granules in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

4. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, placing a weight on the powder granules in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

5. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, placing pressure on the powder granules in the container, admitting a casting solvent into the container through the bottom portion thereof until the powder is substantially covered, and curing the contents within the container to form a large cast propellant.

Alternatively, the propellantmay be cast in a 6. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, placing pressure on the powder granules in the container, admitting a casting solvent into the container through the bottom portion thereof until the powder is substantially covered, removing the pressure from the granules, and curing the contents within the container to form a large cast propellant.

7. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, evacuating the smokeless powder granules to remove surface moisture therefrom, placing a weight on the powder granules in the container, admitting a casting solvent into the container through the bottom portion thereof until the powder is substantially covered, and curing the contents within the container to form a large cast propellant.

8. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing smokeless powder granules into a container, evacuating the smokeless powder granules to remove surface moisture therefrom, placing a weight on the powder granules in the container, admitting a previously evacuated casting solvent into the container through the bottom portion thereof until the powder is substantially covered, and curing the contents within the container to form a large cast propellant.

9. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing an explosive casting powder and a burning rate control powder into a container, placing a weighted member on the powder in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

10. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing an explosive casting powder and a burning rate control powder into a container, placing a weighted member on the powder in the container, admitting a casting solvent into the container through the bottom portion thereof until the powder is substantially covered, and curing the contents within the container to form a cast propellant.

11. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing an explosive casting powder and a burning rate control powder into a container, placing a weighted member on the powder in the container, admitting a casting solvent into the container through the bottom portion thereof until the powder is substantially covered, removing the weighted member from the powder, and curing the contents within the container to form a large cast propellant.

12. In the manufacture of cast smokeless powder propellants, the improvement comprising introducing a mixture of casting powder and burning rate control powder into a container, placing a weighted member on the powder in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

13. In the manufacture of cast smokeless powder propellants, the improvement comprising placing a plurality of strands of burning rate control powder in a container in fixed spaced relation, pouring smokeless powder granules into the container around the strands of burning rate control powder, placing a weighted member on the powder in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

14. In the manufacture of cast smokeless powder propellants, the improvement comprising forming a mixture of smokeless powder granules having burning rate control powder granules uniformly distributed therethrough, introducing the mixture into a container in a manner such that the burning rate control granules remain uniformly distributed throughout the smokeless powder granules, placing a weighted member on the powder in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

15. In the manufacture of cast smokeless powder propellants, the improvement comprising forming an assembly of a plurality of strands of burning rate control powder arranged in parallel spaced relation, placing the assembly in a casting container, pouring smokeless powder granules into the container around the strands of burning rate control powder, placing a weighted member on the powder in the container, and admitting nonvolatile plasticizers to the container through the lower portion thereof.

16. The process of manufacturing cast smokeless powder propellants comprising forming a mixture of smokeless powder granules having burning rate control powder granules uniformly distributed therethrough, introducing the mixture into a container in a manner such that the burning rate control granules remain uniformly distributed throughout the smokeless powder granules, evacuating 12 the mixture to remove surface moisture therefrom, placing a weighted member on the powder in the container, admitting a previously evacuated casting solvent into the container through the bottom portion thereof until the powder is substantially covered, and curing the contents within the container to form a large cast propellant.

References Cited by the Examiner UNITED STATES PATENTS 435,842 9/90 Larnm.

753,959 3/04 Crurnp. 1,870,661 8/32 Vogt. 2,297,248 9/42 Rudolph.

CARL D. QUARFORTH, Primary Examiner.

BENJAMIN HENKIN, REUBEN 'EPSTEIN, Examiners. 

1. IN THE MANUFACTURE OF CAST SMOKELESS POWDER PROPELLANTS, THE IMPROVEMENT COMPRISING INTRODUCING SMOKELESS POWDER GRANULES INTO A CONTAINER, PLACING PRESSURE ON THE POWDER GRANULES IN THE CONTAINER, AND ADMITTING NONVOLATILE PLASTICIZERS TO THE CONTAINER THROUGH THE LOWER PORTION THEREOF. 